let addition = function(a, b) {
    return a + b;
}

let subtract = function(a, b) {
    return a - b;
}

let divide = function(a, b) {
    return a / b;
}

let multiply = function(a, b) {
    return a * b;
}

console.log(module.exports === exports);

console.log('导出前: ', exports);

// 使用 exports 导出本模块中需要对外暴露的变量
// exports.add = addition;
// exports.sub = subtract;
// exports.div = divide;
// exports.mul = multiply;

module.exports.add = addition;
module.exports.sub = subtract;
module.exports.div = divide;
module.exports.mul = multiply;

console.log('导出后: ', exports);